Currently known alloys based on metals of Group VIII and nitrides of metals of Groups III through VII employed as alloying materials have low unsatisfactory properties. Usually these alloys contain 3 to 17% of nitrogen, have density of from 2 to 5 g/cm.sup.3, porosity of from 30 to 60%, crushing strength below 2 kg/mm.sup.2. These alloys comprise either a powder or a loose sintered briquette. Nitrogen distribution in these alloys is extremely non-uniform. It is usually combined in large-size nitrides with particles of up to 2 mm which are present in the alloy as individual inclusions non-bonded therebetween.
A low density of the above-mentioned alloys, their high porosity and a non-uniform distribution of nitrogen in the form of large-size nitrides cause a low degree of assimilation of nitrogen by steel and a non-uniform distribution thereof within the ingot volume. A low mechanical strength of the alloys and their powder-like state result in considerable losses of the alloy during operations of alloying, transportation and conditioning, as well as in a sharply lowered degree and stability of assimilation of nitrogen by steel.
To produce the above-mentioned alloys, at the present time alloys are obtained which contain metals of Groups III-VII and iron. Usually the starting alloys are disintegrated to powder, placed into the nitrogen-containing atmosphere, heated to a temperature within the range of from 500.degree. to 1,100.degree. C. and maintained at this temperature for several hours.
These prior art processes feature a high rate of electric power consumption, a long duration of the process and a low quality of the resulting alloys. The alloys produced by these processes usually necessitate an additional processing, i.e. briquetting and sintering.
Thus, known in the art is an alloy based on iron and nitrides of manganese and chromium. To produce this material use is made of an alloy of iron with manganese and chromium which is disintegrated to powder with a particle size of below 2 mm and subjected to nitriding for 4 hours at the temperature of 900.degree. C. The content of nitrogen is 4 to 6%. The resulting powder is additionally briquetted (cf. Japanese Pat. No. 27321, Cl. 10 A 12, 1965).
To obtain a higher content of nitrogen in the alloy, a step-wise nitriding process is employed. In accordance with this process, the starting alloy of iron with manganese is ground to powder with a particle size of below 5 mm, heated for 2 to 4 hours to the temperature of 1,000.degree. C.; the resulting sintered mass is again crushed to powder and subjected to nitriding by passing ammonia for 6-10 hours at a temperature within the range of from 500.degree. to 700.degree. C. The thus-produced powder contain 9 to 11% of nitrogen (cf. Swedish Pat. No. 335,235, 1971).
Known in the art is a process for producing alloys based on iron and nitrides of metals of Groups III-VII, wherein the starting alloy containing two metals of III-VII Groups is employed for intensification of the process and a high content of nitrogen. For example, the starting alloy of iron with chromium and aluminium is ground to powder with a particle size of below 60 mm and subjected to nitriding in the atmosphere of nitrogen or ammonia for 5 hours at the temperature 1,000.degree. C. After nitriding the powder contains up to 9.8% of nitrogen (cf. Japanese Pat. No. 25892 Cl. 10N 16, 1964).
Known is another process for producing alloys based on iron and nitrides of metals of Groups III-VII, wherein use is made of the starting alloy incorporating two metals of III-VII Groups. The starting alloy of iron with vanadium and manganese is ground to powder and heated to a temperature within the range of from 900.degree. to 1,100.degree. C. with nitrogen supply for 8 hours without fusing. The resulting powder contains 6 to 17% of nitrogen. Then it is subjected to briquetting using 2 to 10% of a binder (cf. U.S. Pat. No. 3,304,175, 1967).
Known is a process for producing alloys based on iron and nitrides of vanadium, niobium, chromium and manganese. The starting alloys of iron with vanadium, niobium, chromium and manganese are ground to powder with a particle size of below 0.3-0.6 mm and saturated with nitrogen at a temperature of above 800.degree. C. The resulting powder-like alloy contains 3.4 to 11.1% of nitrogen (cf. FRG Pat. No. 1,558,500, 1971).
The above-discussed alloy based on iron and nitrides of metals of III to VII Groups are produced as a powder-like material with an extremely non-uniform distribution of nitrogen.
Known in the art is a process for producing the above-mentioned alloys, wherein for the uniform distribution of nitrogen the process is carried out in rotating tubular furnaces at a temperature within the range of from 700.degree. to 1,100.degree. C. However, in this case the material is also produced as a powder which is hardly suitable for use without additional processing (cf. GDR Pat. No. 54,815, 1967).
The above-listed processes demonstrate that at the present time there is lack of processes resulting in the production of alloys based on metals of Group VIII and nitrides of metals of III-VII Groups with a density of more than 5 g/cm.sup.3, porosity below 30%, crushing strength above 5 kg/mm.sup.2, relative wear of below 15, nitride particle size of below 0.1 mm at a content of nitrogen of above 5% and uniform distribution of the latter.
There is known a process for producing high-melting inorganic compounds, wherein at least one metal of IV-VI Groups is mixed with one of non-metals selected from the groups of carbon, nitrogen, boron and silicon, oxygen, phosphorus, fluorine chlorine and an ignition agent is introduced into the resulting mixture to create the temperature necessary to initiate burning of the initial components which further interact due to the heat evolved during the reaction (cf. U.S. Pat. No. 3,726,643, 1973).
This process covers the production of powders of refractory inorganic compounds such as nitrides of zirconium, titanium, niobium. The melting point of these nitrides is substantially higher than their burning temperature, i.e. the temperature which is developed in the reaction of interaction between titanium, niobium and zirconium with nitrogen by the above-mentioned process, wherefore it is impossible to obtain a compact material by this process. At best, it is possible to obtain briquettes with a density equal to that of the starting powder (2-4 g/cm.sup.3).
It is neither possible to obtain a compact material by the prior art process by introduction of metals of VIII Group into the initial mixture of powders. In this case, due to the formation of local fused regions, the density of the resulting briquettes can be increased to 4.5-5.0 g/cm.sup.3, which, however, results in a very non-uniform distribution of nitrogen reaching 50-100%. The fused regions usually alternate with shells and voids, wherefore the crushing strength of the resulting briquettes is very small and does not reach even 5 g/m.
Therefore, the above-mentioned process does not ensure the production of alloys based on metals of Group VIII and nitrides of metals of Groups III-VII with a density above 5 g/cm.sup.3, porosity below 30%, crushing strength above 5 kg/mm.sup.2, relative wear below 15 units (1 unit--relative wear of tungsten carbide), nitride particle size of below 0.1 mm, at a content of nitrogen above 5% and non-uniformity of nitrogen distribution 10% with non-uniformity of nitrogen distribution of below 10% in the case of using the starting metals as individual elements.